A mining magnate has told a corruption inquiry he wanted the Obeid family name removed from a project because it always attracted bad publicity.

The Independent Commission Against Corruption (ICAC) is investigating allegations former NSW mining minister Ian Macdonald rigged tenders for mining projects and made decisions that could have generated a $100 million profit for colleague Eddie Obeid and his associates.

Mining billionaire Travers Duncan has been grilled at the ICAC about his stake in Cascade Coal and his knowledge of mining tenders in the Bylong Valley near Mudgee.

Mr Duncan has denied getting top-secret government information from Mr Macdonald and denied leaking that information to others.

After he hesitated in answering several questions, the Counsel-Assisting, Geoffrey Watson, asked the witness if he assumed he was a mug. Mr Duncan also denied that.

Mr Duncan has admitted he wanted the Obeid name removed from a mining project.

Mr Watson asked: "Why did you try to get rid of the Obeids?"

After hesitating and hedging around the question, Mr Duncan eventually said: "They always had bad publicity."

Mr Watson then became angry and snapped: "What were they famous for?" adding, "Was it because of their cheap suits?"

Mr Duncan replied: "It was a name I didn't like, and I didn't want to do business with them."

The ICAC has previously heard the Obeids had a 25 per cent hidden stake in Cascade Coal.

The inquiry was then played secretly recorded phone conversations between Mr Duncan and a colleague negotiating a mining deal.

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